A level has been utilized in various industrial fields in recent days, and it is especially practical for use in transportation equipments like automobiles or aircrafts. As is well known, it is quite common to use a bubble tube and stick type level. This type of level is devised of a liquid having a bubble, contained and sealed into a curved glass tube, wherein the bubble is adapted to stay at the center of the tube when the tube is kept horizontal.
This type of level is an indispensable apparatus for obtaining a level line or horizontal surface, and for instance, in the U.S.A., this level is required to be equipped on the upper part of the headlight of every car. Through the equipment of this level, the correct direction of the headlight is confirmed, keeping the headlight not too high or too low.
It is normally seen that the level to be equipped with the headlight contains and seals some chemical compound made from methyl alcohol or silicon oil-20, and also a very small quantity of fluorescent dyestuff is mixed therein.
The prior levels of the bubble tube and stick type, which are mainly used with the headlight of a car, have the following defects.
It is a common concern that a glass tube can expand and be broken by the heat generated by the headlight or a traffic collision may occasion the breaking of the glass tube. In the cases where the level contains methyl alcohol, since methyl alcohol is combustible, it ignites by itself in accidents, or else it can promote a fire.
On the other hand, in the case of the level containing silicon oil-20, the viscosity of this substance is so high at 20.0 centistokes (hereinafter as referred to "cSt") that it easily occasions bubble cracking when shocked which causes unstable measuring.
The above explained defects mainly occur in the glass tube and stick type level, but of course similar defects are also seen in other types of the levels.
In order to overcome these defects, the present inventor has been studying and investigating in various fields, so that he can find more preferable chemical substances which are very similar to methyl alcohol but are in incombustible, and they may also satisfy the following requirements:
1. No bubble cracking occurs when the glass tube receives a shock, and even if such cracking happens, it restores immediately to the normal condition. PA0 2. The bubble moves smoothly. PA0 3. It can be handled safely without any danger of a toxic or poisonous quality. PA0 4. It is smoothly soluble to dyestuff. PA0 5. It is strongly resistant to changes in temperature. PA0 6. It is easy to obtain.
As a result of his deep study and effort, the inventor has found a substance of chlorofluorocarbon (hereinafter as referred to "CFC") which meets the above requirements. However, this substance, CFC, is said to destroy the ozone atmosphere, and therefore it is likely to be forbidden for use in the future.
The inventor, therefore, has been continuing his study to seek another substance which satisfies all the conditions discussed above, and finally, through his investigation, he has come to know that a desirable substance can be obtained by mixing the fluorine chemical compound as a main agent with an additive agent, whereby the defects are prevented by the effect of the additive agent. Based on this knowledge, he has succeeded in providing a desirable level erasing the prior defects.